[RailsConf 2019] Troubleshoot Your RoR Microservices with Distributed Tracing

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©2019 Wantedly, Inc. Tokyo based company. We “create a world where work drives passion,” by helping people uncover jobs they are passionate about, visit future teammates who share the same values, and meet an exciting company they’ll love working for.

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©2019 Wantedly, Inc. • A trace is a set of operations in an end-to-end request. • A trace has spans. A span represents an operation. • Spans can be nested, which represents causality. • A span has a name, and contains start and end time with other annotations. Distributed Tracing

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©2019 Wantedly, Inc. 1. Libraries for tracing and metrics • Java, Go, Node, Python, C++, C#, PHP, Ruby, Erlang/Elixir • Focus on capturing and sending data in your app, no analysis part provided. 2. Exporter for backend(s) of your choice • Send to StackDriver, DataDog, Jaeger, Zipkin, Prometheus, etc. • Can export to multiple backends at once. 3. Out-of-box integrations • Rack middleware for inbound request, Faraday middleware for outbound request. • Instrument events like ActiveRecord database calls, ActionView renders, etc OpenCensus

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©2019 Wantedly, Inc. • trace_id: a 16-byte unique identifier for a trace. • span_id: a 8-byte unique identifier for a span. • parent_span_id: span_id of this span's parent span. • name: a description. Can be a method name, or a file name and a line num. • kind: UNSPECIFIED, SERVER, or CLIENT. • start_time, end_time: when a span starts and ends. • attributes: a set of key-value pairs. Value can be string, integer, double or bool. • stack_trace: A stack trace at the start. • time_events: a time-stamped annotation or send/rcv message event in a span. • links: a pointer from the current to another span in the same or a different trace. • status: a finally status of the span Span See https://github.com/census-instrumentation/opencensus-proto/blob/master/src/opencensus/proto/trace/v1/trace.proto

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©2019 Wantedly, Inc. # Gemfile gem 'opencensus' # When a process starts OpenCensus.configure do |c| c.trace.middleware_placement = :begin c.trace.exporter = exporter c.trace.default_sampler = \ OpenCensus::Trace::Samplers::Probability.new(0.01) c.trace.default_max_attributes = 64 end Configure Tracing

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©2019 Wantedly, Inc. # DataDog exporter uri = URI.parse(ENV['DATADOG_APM_AGENT_URL']) c.exporter = OpenCensus::Trace::Exporters::Datadog.new \ service: app_name, agent_hostname: uri.host, agent_port: uri.port # StackDriver exporter keyfile = Base64.strict_decode64(ENV['STACKDRIVER_JSON_KEY_BASE64']) c.exporter = OpenCensus::Trace::Exporters::Stackdriver.new \ project_id: gcp_project_id, credentials: JSON.parse(keyfile) # multiple exporters c.exporter = OpenCensus::Trace::Exporters::Multi.new(*exporters) Configure Exporter

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©2019 Wantedly, Inc. Rails Integration # application.rb require 'opencensus/trace/integrations/rails' # <- Rails::Railtie # the toplevel configuration object is exposed as `config.opencensus` config.opencensus.trace.default_max_attributes = 64

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©2019 Wantedly, Inc. class OpenCensus::Trace::Integrations::RackMiddleware def call env formatter = Formatters::TraceContext.new context = formatter.deserialize env[formatter.rack_header_name] Trace.start_request_trace \ trace_context: context, same_process_as_parent: false do |span_context| begin Trace.in_span get_path(env) do |span| start_request span, env @app.call(env).tap do |response| finish_request span, response end end ensure @exporter.export span_context.build_contained_spans end end end end Rack Middleware

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©2019 Wantedly, Inc. DEFAULT_NOTIFICATION_EVENTS = [ "sql.active_record", "render_template.action_view", "send_file.action_controller", "send_data.action_controller", "deliver.action_mailer" ].freeze def setup_notifications OpenCensus::Trace.configure.notifications.events.each do |type| ActiveSupport::Notifications.subscribe(type) do |*args| event = ActiveSupport::Notifications::Event.new(*args) handle_notification_event event end end end ActiveSupport::Notification

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©2019 Wantedly, Inc. def handle_notification_event event span_context = OpenCensus::Trace.span_context if span_context ns = OpenCensus::Trace.configure.notifications.attribute_namespace span = span_context.start_span event.name, skip_frames: 2 span.start_time = event.time span.end_time = event.end event.payload.each do |k, v| span.put_attribute "#{ns}#{k}", v.to_s end end end ActiveSupport::Notification (cont) See https://api.rubyonrails.org/classes/ActiveSupport/Notifications.html

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©2019 Wantedly, Inc. class OpenCensus::Trace::IntegrationsFaradayMiddleware < ::Faraday::Middleware def call request_env span_context = request_env[:span_context] span_name = extract_span_name(request_env) span = span_context.start_span span_name, sampler: @sampler start_request span, request_env begin @app.call(request_env).on_complete do |response_env| finish_request span, response_env end rescue StandardError => e span.set_status 2, e.message raise ensure span_context.end_span span end end end Faraday Middleware

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©2019 Wantedly, Inc. conn = Faraday.new(url: api_base_url) do |c| c.use OpenCensus::Trace::Integrations::FaradayMiddleware, span_name: ->(env) { env[:url].path } c.adapter Faraday.default_adapter end Faraday Middleware (cont) Recommend to do this in a private gem used in your rails apps.

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©2019 Wantedly, Inc. Custom Span API OpenCensus::Trace.in_span "long task" do t = rand * 10 sleep t end def in_span name, kind: nil, skip_frames: 0, sampler: nil span = start_span name, kind: kind, skip_frames: skip_frames + 1, sampler: sampler begin yield span ensure end_span span end end